Great topic, Sudhakar! Let's explore packages in Java — they're essential for organizing code, avoiding name conflicts, and building clean, modular applications.

📦 What is a Package in Java?

A package in Java is a namespace that organizes related classes and interfaces.

You can think of it like a folder in your computer that holds similar files — it helps keep your codebase clean and manageable.

✅ Types of Packages

1. Built-in Packages

Provided by Java itself.

Examples:

  • java.lang (default – includes String, Math, etc.)
  • java.util (collections, date/time, etc.)
  • java.io (file input/output)
  • java.sql (database connectivity) 
import java.util.Scanner; // importing built-in class

2. User-defined Packages

You can create your own packages to group related classes.

🧠 Creating and Using a Package

🔨 Step 1: Create the Package

File: MyClass.java

package mypackage;

public class MyClass {
    public void display() {
        System.out.println("Hello from MyClass in mypackage!");
    }
}

Note: The package line must be the first line of code.

🔗 Step 2: Use the Package in Another File

File: Test.java

import mypackage.MyClass;

public class Test {
    public static void main(String[] args) {
        MyClass obj = new MyClass();
        obj.display();
    }
}

⚙️ Compile & Run (Command Line): 

javac -d . MyClass.java   // creates folder structure for package
javac Test.java
java Test

🧾 Benefits of Using Packages

Benefit Description
✅ Organization Helps group related classes
✅ Avoids name conflicts Two classes with the same name can live in different packages
✅ Access control Use public, private, protected, and default access wisely
✅ Code reusability Easier to import and reuse functionality

🔐 Access Modifiers with Packages

Modifier Same Class Same Package Subclass (Other Package) Other Package
public ✅ ✅ ✅ ✅
protected ✅ ✅ ✅ ❌
no modifier ✅ ✅ ❌ ❌
private ✅ ❌ ❌ ❌

🎯 Real-World Example:

  • com.bank.accounts.SavingsAccount
  • com.bank.transactions.TransferService

These packages help break down a project into meaningful modules.